1. Field of the Invention
The invention relates to display devices, and in particular to color electrowetting display devices.
2. Description of the Related Art
Electrowetting display devices are rendered images in accordance with electrowetting or electrocapillary. Briefly, the free surface energy of some fluids is changed due to electric field effects such that distribution area of the fluids can thus change along with the electric field effects.
U.S. Pat. No. 6,967,763, the entirety of which is hereby incorporated by reference, discloses an electrowetting display device. An opaque non-polar fluid in the electrowetting display device converges due to electrowetting effect, thereby controlling a bright state and/or a dark state of a pixel.
FIGS. 1A and 1B are cross sections respectively illustrating a voltage off-state and a voltage on-state for a conventional electrowetting display. Referring to FIG. 1A, a conventional electrowetting display 10 includes a substrate 11 with a patterned pixel electrode 12 disposed thereon. A dielectric layer 13 having a hydrophobic surface is disposed on the patterned pixel electrode 12. Patterned hydrophilic bank structures 14 are disposed on the dielectric layer 13, thereby defining each of pixel regions. An opaque non-polar fluid 15a containing a black dye and transparent polar fluid 16 are disposed in each pixel region. When the applied voltage is “off”, the opaque non-polar fluid 15a uniformly distributes in a pixel region, thereby rendering the pixel region to display a dark state.
On the contrary, when the applied voltage is “on”, the transparent polar fluid 16 is affected by electrowetting force to approach the pixel electrode and the opaque non-polar fluid 15b is converged far away from the pixel electrodes 12. A large portion of the pixel region is thus exposed, thereby rendering the pixel region to display a bright state, as shown in FIG. 1B.
FIG. 2 is a cross section schematically illustrating a conventional single-layered color electrowetting display device. In FIG. 2, a single-layered color electrowetting display device 50 includes a first substrate 51 and a second substrate 61 opposing to each other. The first substrate 51 includes patterned electrodes 52 corresponding to each of sub-pixel regions. A reflective layer 53 is disposed on the patterned electrode 52. A partition structure 54 is disposed on the reflective layer 53, thereby defining an array of sub-pixels. A black-dye containing first fluid 55 is disposed on the patterned electrodes 52 in each of the sub-pixels. A transparent second fluid 56 is filled between the first substrate 51 and the second substrate 61. A color filter 62 including red 62R, green 62G, and blue 62B color units is disposed on the second substrate 61. Each of the red 62R, green 62G, and blue 62B color units is corresponding to a sub-pixel region. A seal structure 70 is formed on the peripheral region of the display device encapsulating the first substrate 51 and the second substrate 61. A common electrode 65 contacts the second fluid 50. The surface tension of the first fluid 55 and the second fluid 50 are changed due to electrical field generated between the common electrode 65 and electrodes 52 in each sub-pixel region, thereby rendering display images. Specifically, whether the ambient light passing through the display device is reflected or absorbed is depended from shrink or stretch of the black non-polar fluid. The reflective light passing through the color filter on the first substrate is converted into desirable color of light to achieve full color display.
WO 2003/071347, the entirety of which is hereby incorporated by reference, discloses a color electrowetting display structure. FIG. 3 is a cross section of a tri-layered color electrowetting display device. Referring to FIG. 3, in the structure of the tri-layered color electrowetting display device 100, a partition structure 113 defined a plurality of sub-pixel structures between the upper and lower substrate. Polar fluid 106 and corresponding two different color non-polar ink oils 105W, 105C, 105Y, and 105M are filled into each sub-pixel structure, wherein a polar fluid is sandwiched between two non-polar ink oils such that a tri-layered structure consisting of ink oil, polar fluid and ink oil is presented between the upper and lower substrates. A color filter 121 is disposed on the upper substrate. The color filter has a complementary color with the other two different colors of the non-polar ink oils. During operation, different bias are respectively applied on electrodes 112 and 132-137, and whether the different non-polar ink oils are shrink or stretch can affect incident light 116 by the reflective plate 122 or is absorbed by different color non-polar ink oils 105W, 105C, 105Y, and 105M. The reflected light pass through color units 121M, 121C, and 212Y of the color filter thereby rendering desirable light colors.
The conventional single-layered color electrowetting display structure, however, uses color filter associated with black non-polar fluid (such as ink oil). Part of incident light is absorbed by the color filter resulting in lower color efficiency and saturation. Contrast ratio and brightness of the display images are also reduced. In addition, alignment between the color filter substrate and the lower substrate is so difficult that fabrication complexity of the display device is also increased. On the other hand, although conventional tri-layered color electrowetting display device can effectively improve color saturation, the display structure is complex, fabrication processes are tedious, and production cost is very high.